Resonance-assisted light–control–light characteristics of SnS 2 on a microfiber knot resonator with fast response

An all-optical light–control–light functionality with the structure of a microfiber knot resonator (MKR) coated with tin disulfide (SnS2) nanosheets is experimentally demonstrated. The evanescent light in the MKR [with a resonance Q of ∼59,000 and an extinction ratio (ER) of ∼26  dB] is exploited to enhance light–matter interaction by coating a two-dimensional material SnS2 nanosheet onto it. Thanks to the enhanced light–matter interaction and the strong absorption property of SnS2, the transmitted optical power can be tuned quasi-linearly with an external violet pump light power, where a transmitted optical power variation rate ΔT with respect to the violet light power of ∼0.22  dB/mW is obtained. In addition, the MKR structure possessing multiple resonances enables a direct experimental demonstration of the relationship between resonance properties (such as Q and ER), and the obtained ΔT variation rate with respect to the violet light power. It verifies experimentally that a higher resonance Q and a larger ER can lead to a higher ΔT variation rate. In terms of the operating speed, this device runs as fast as ∼3.2  ms. This kind of all-optical light–control–light functional structure may find applications in future all-optical circuitry, handheld fiber sensors, etc.